In manufacturing semiconductor devices, various processes, such as film formation, quality modification, oxidation/diffusion, etching and the like, are performed on a semiconductor wafer as a substrate to be processed.
For the film formation, there is widely used a CVD (Chemical Vapor Deposition) method for forming a predetermined film through a chemical reaction by introducing a predetermined processing gas into a chamber accommodating a semiconductor wafer. In the CVD method, a film is formed by the reaction of the processing gas on the semiconductor wafer as a substrate to be processed. At this time, however, only 10% of the processing gas contributes to the reaction, and most of the processing gas remains unreacted.
The unreacted processing gas reacts with a reaction gas in the chamber or in a gas exhaust pipe into which the reaction gas is introduced, to produce a by-product. The by-product thus produced flows together with a by-product produced when forming a TiN film. When the by-products are cooled, a pipe is clogged or a vacuum pump is damaged. To that end, in general, a trap mechanism for trapping a by-product is provided at the gas exhaust pipe extending from the chamber.
Although it is preferable that the by-product is trapped by the trap mechanism in the form of a compound that is easily trapped and has a comparatively stable structure, the by-product produced at a flow rate ratio of each processing gas for film formation is not necessarily turned into a desired compound. Therefore, Japanese Patent Laid-open Publication No. 2001-214272 discloses a technique for producing a trappable by-product by introducing directly into a trap mechanism or into an upstream pipe a reaction gas that reacts with an impurity gas discharged from the chamber.
In theory, a desired stable by-product that is easily trapped can be produced by introducing a specific reaction gas. In practice, however, the reaction may proceed insufficiently, so that an unstable by-product or a by-product having an indefinite structure such as a complex or the like may be produced. Accordingly, the trap mechanism needs to be scaled up due to hard to trap the by-product and, also, the trap mechanism may be irregularly clogged due to an unreliable generation state (density or the like) of a reaction product.